In telecommunication networks, protection refers to the ability to recover protected traffic in the case of a failure by switching over automatically to a redundant resource. For TDM-based transport networks, sophisticated protection mechanisms have been described and defined. The basic standard in SDH (Synchronous Digital Hierarchy) that describes types and characteristics of protection architectures is ITU-T G.841 (October 1998), which is incorporated by reference herein.
A basic topology in protected networks is a ring network. In order to avoid misconnections in a ring protection scheme in the case of a double failure, a mechanism known as “squelching” has been developed for SDH rings. Squelching implies that the traffic addressed to nodes that are isolated due to a double failure occurring in the ring is ‘squelched’ at switching nodes, i.e. replaced or overwritten with AIS (Alarm Indication Signal). A switching node is any node that performs a bridge or switch function for a protection event. The generalized squelching logic is defined in G.841 Appendix II.
In order to make squelching work properly in a TDM ring it is required to configure each node in the ring with a ring map. Each of the ring maps must contain information regarding the order in which the nodes appear on the ring. In addition each node requires a connection map that contains the AU-4 time-slot assignments for traffic that is both terminated at that node and passed-through that node and a squelch table that identifies for each of these AU-4 time slots the node addresses at which the traffic enters and exits the ring.
Today, packet transport networks as opposed to classical TDM networks are emerging. Protocols for packet transport are currently under development, one of which is referred to as T-MPLS (Transport MultiProtocol Label Switching). Transport MPLS is a purely connection-oriented packet transport network based on MPLS that provides managed connections to different packet client layer networks.
Hence, protection mechanism and strategies for packet transport networks need to be defined. Packet ring technologies could possibly reuse the above mentioned protection techniques known from TDM networks. However, a direct adoption of TDM methods to packet transport network would not provide efficient bandwidth usage.
In a TDM network, a connection (e.g. a VC-4 timeslot) actually determines the bandwidth this connection occupies, regardless of the amount of user traffic currently transmitted over this connection. This means that since a TDM connection needs to be pre-provisioned, its bandwidth cannot be effectively used by other connections.
Conversely, in packet technology, a connection (e.g. a T-MPLS label) specifies a route through the network but it does not determine the bandwidth which is actually occupied by user traffic transmitted on this connection. The total amount of bandwidth in a packet network can be effectively shared between different connections not only at the provisioning stage but also during network operation in both normal and protection situations.
Moreover, it is expected that in T-MPLS rings the number of connections could reach more that ten thousands. This would increase the complexity and require a long time for the configuration (e.g., via network management or local crafts personnel) of all nodes in the ring through which these connections are passing and may make the target protection time of 50 ms difficult to achieve.
The squelching mechanism in TDM developed for misconnection avoidance does not address the variable bandwidth nature of packet traffic and does not address the scalability problem, which arises due to the high number of connections in the packet ring. The inherent constrains of TDM technology when applied to packet rings would lead to inefficient bandwidth resource usage; configuration scalability issue; and increased protection switching time.
In view of the above discussed constraints, it is a problem of the present invention to provide a method and corresponding apparatus for providing packet ring protection.